The present invention relates to an ohmic electrode of a semiconductor device employing a silicon carbide (SiC) substrate and a method of manufacturing the ohmic electrode.
An important factor in lowering the ON-resistance of a power device employing SiC is lowering the contact resistance and the resistance of wiring. To realize low ON-resistance, a related art divides a main electrode area of a power device into small sections and densely arranges the divided sections on an SiC substrate. To reduce the ON-resistance of such a fine power device, what is required is to stabilize and decrease the contact resistance ρc and wiring resistance of an opening (contact hole) formed through an insulating film. Reducing these resistance values relative to that of the SiC region is also important to improve the switching speed of the power device.
A related art widely used for forming a low-resistance ohmic contact employs nickel (Ni), tungsten (W), titanium (Ti), aluminum (Al), or the like as an electrode film raw material, deposits the raw material over a high-concentration impurity region on an SiC substrate, heat-treats the substrate at a high temperature of 800° C. to 1200° C. to cause a solid phase reaction between the raw material and SiC, and thereby forms a thermally-reacted layer between the raw material and the high-concentration impurity region. The area between the thermally-reacted layer and the high-concentration impurity region has a proper ohmic property. An ohmic contact employing Ni among the raw materials can provide a contact resistance value ρc on the order of 10−6 Ωcm2 that is practical for an n-type SiC region. This is a promising ohmic contact. For a p-type SiC region, an ohmic contact made from a multilayer film of, for example, Ti/Al is usable. Examples of ohmic electrodes employing an Ni film are disclosed in Japanese Laid-open Patent Publications No. Hei-8-64801 and No. 2002-93742.